We continue to study the incidence and specificity of placental proteins (chorionic gonadotropin and its free alpha and beta subunit, placental lactogen, and placental alkaline phosphatase) as cancer markers in vivo and in vitro. These proteins appear to distinguish cancers from benign tumors and their concentrations in plasma often correlate with the response to therapy. Various permanent cell lines have been established to study the prevalence of ecotopic placental protein and subunit production, the regulation of placental protein synthesis in vitro and to characterize the properties of these materials as well as their in vitro response to chemotherapeutic agents. Immunocytochemical techniques have been developed to localize the cells responsible, in heterogeneous tumors, for ectopic placental protein and subunit production. BIBLIOGRAPHIC REFERENCES: Lieblich, J.M., Weintraub, B.D., Krauth, G.H., Kohler, P.O., Rabson, A.S. and Rosen, S.W.: Ectopic and eutopic secretion of chorionic gonadotropin and its subunits in vitro: Comparison of clonal strains from carcinomas of lung and placenta. J. Natl. Cancer Inst. 56: 911-917, 1976. Lieblich, J.M., Weintraub, B.D., Rosen, S.W., Ghosh, N.K. and Co, R.P.: Secretion of HCG-alpha subunit and HCG by HeLa strains. Nature 265: 746, 1977.